Automatic transmissions of vehicles use a one way clutch that transmits torque of the driving side when rotating in one direction and does not transmit torque when rotating in the reverse direction.
An example of conventional one way clutches is shown in FIG. 7. This one way clutch comprises an inner ring 103, an outer ring 105 disposed coaxially with the inner ring 103, a plurality of cam surfaces 113 provided along the circumferential direction on the inner circumferential surface of the outer ring 105, each including a recessed portion 109 and a slope 111, torque transmission members 107 interposed between the cylindrical surface on the outer circumference of the inner ring 103 and the aforementioned cam surfaces 113, biasing members 117 that bias the respective torque transmission members 107 against the slopes 111 of the cam surfaces 113, and a retainer 123 that retains the torque transmission members 107 and the biasing members 117.
When the inner ring 103 rotates in one direction, the biasing members 117 biases the torque transmission members 107 against the slopes 111 of the corresponding cam surfaces 113. Thus, the torque transmission members 107 are made integral with the inner ring 103 and the outer ring 105 to transmit torque. On the other hand, when the inner ring 103 rotates in the reverse direction, the torque transmission members 107 compress the corresponding biasing members 117 to enter the recessed portions 109 of the corresponding cam surfaces 113. This allows relative rotation of the inner ring 103 and the outer ring 105, resulting in idle rotation of the inner ring 103 and disabling torque transmission. FIG. 8 is an enlarged partial view showing the relevant portion of the above-described conventional one way clutch in a sub-assembly state, namely showing an intermediate assembly that has not been assembled to an automatic transmission or other equipment yet.
Japanese Patent Application Laid-Open No. 2004-308719 discloses a one way clutch in which a gap is provided between an engagement projection that is provided on the radially outward end face of a block bearing facing the outer ring and a retaining groove that is provided on the outer ring to engage the engagement projection, in order to prevent a torque transmission member from overrunning to damage a retainer when excessively high torque is input.